BROAD-BAND HIGH-OPTICAL-DENSITY FILTERS IN THE INFRARED

A new concept for the design of broadband (2-25 mu m and beyond) neutral-density filters in the infrared region without etaloning effects is proposed and demonstrated. One important aspect of the technique is to use metallic-thin-film (10-200-nm-thick) multilayer combinations deposited onto different substrates (ZnSe, CdTe, Lexan). Neutral-density filters with optical densities as high as 4 are designed and built in the broadband region (2-25 mu m). Another key innovation is the use of ultrathin substrates (similar to 100 nm thick) for elimination of etaloning effects normally present in thick (>0.5-mm) substrates. Neutral-density filters with such ultrathin substrates are also designed and investigated.